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    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
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<body>
<script>
    //1,2,3
    // 异步，变同步
    console.log(1);
    // Promise 异步任务同步化
    // 许诺 Promise 包含一个耗时性的任务
    const p = new Promise((resolve) => {
        // 执行
        setTimeout(function(){
        console.log(2);
        resolve();
        },3000)
    })
    p.then(() => {
    console.log(3);
    })

    console.log(4);
</script>
</body>
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